The optical sensor achieves its sense function generally by measuring the change of intensity or the phase of the light beams. Compared to conventional sensor types, the optical sensor enjoys the advantages such as great sensitivity, wide dynamic sense range and multiplexing capabilities. In recent years, MEMS technology is widely used on the design of optical sensor due to the small feature of MEMS, which could be high sensitive with tiny change of the detected objective. In this paper, instead of observing the change of intensity and phase, the author studied how the shift of wavelength spectrum can be utilized to sense the physical change of the object such as the pressure, vibration, velocity and electrical field. The author designed and simulated a FP-resonator-like structure which consists of 2 resonant cavities with 2 multi-layer mirrors located on two ends and 1 multi-layer mirror in the middle of the two cavities. The mirror in the middle is movable by physical pressure. In the simulation, it was found that this structure is able to have certain wavelength light resonate inside the cavities. The resonant mode will shift 1nm when the mirror in the center moves forward/backward for every 14nm, which is sensitive enough to detect the small change of the objectives.